A piezoelectric device, such as a piezoelectric resonator and a piezoelectric oscillator, is widely used in compact information-processing devices, mobile communication devices, piezoelectric gyro sensors, and the like. A compact information-processing device is, for example, a hard disk drive (HDD), a portable computer, or an integrated circuit (IC) card. A mobile communication device is, for example, a mobile phone, a car phone, or a paging system.
FIG. 14 is a schematic planar view of an example of the piezoelectric resonator element that has been used in the piezoelectric device.
With reference to the diagram, an outer shape of a piezoelectric resonator element 1 shown in the diagram is formed by a piezoelectric material being etched. The piezoelectric material is, for example, quartz crystal. The piezoelectric resonator element 1 includes a rectangular base section 2 and a pair of resonating arms 3 and 4. The base section 2 is attached to a package (not shown) or the like. The resonating arms 3 and 4 extend upward from the base section 2, with reference to the diagram. Long grooves 3a and 4a are formed on main surfaces (front and back surfaces) of the resonating arms. A required electrode for driving is also formed on the main surfaces of the resonating arms (refer to Patent Document 1).
In the piezoelectric resonator element 1, such as that described above, a signal of a predetermined frequency is extracted when driving voltage is applied via the electrode for driving, as a result of flexural vibration. In flexural vibration, respective tips of the resonating arms 3 and 4 draw close to and away from each other.
An extraction electrode is formed on such piezoelectric resonator element 1 in areas of the base section 2 indicated by reference numerals 5 and 6. Adhesives 7 and 8 are applied to the areas. The areas are bonded and fixed to, for example, an inner bottom surface of a rectangular, box-shaped, ceramic package. Thus, the extraction electrode is housed therein.
After the piezoelectric resonator element 1 is bonded and fixed using the adhesives, cut portions 9 and 9 are formed on the base section 2 so that residual stress does not interfere with the flexural vibration of the resonating arm. The residual stress remains due to, for example, a difference in coefficients of linear expansion between a material forming the piezoelectric resonator element and a material forming the package and the like.
[Patent Document 1] JP-A-2002-261575
[Patent Document 2] JP-A-2000-68780